1. Field of the Invention
This invention relates generally to hypodermic syringes, and more particularly to such syringes having retractable needles after use to prevent hazardous needle sticks.
2. Description of the Related Art
The idea of safety syringes with retractable needles to prevent needle sticks is well known. Initially such devices were bulky, expensive to manufacture and did not function well. Over the years as the art progressed they became easier to make and operate, but still problems remain which have prevented mass manufacture and use of safety syringes.
Disposable syringes are typically made by automated, high volume plastic injection molding processes. Since these devices by design are disposable after one use, they must be very inexpensive to produce on a per unit basis. The critical parts of the syringe must be structurally sound and well made. Given the uses of syringes in administering drugs, stringent quality standards must be maintained.
Mazur U.S. Pat. No. 5,401,246 disclosed a retractable syringe with a needle holder and needle in a frangible connection in the forward end of a syringe barrel. This syringe includes an additional part, a clip at the forward end of the barrel, which locks the needle holder in place and prevents inadvertent release from the forward end of the barrel. To release the needle holder the user must manually manipulate the clip near the needle, to unlock the needle holder and allow its retraction into the barrel. This manipulation near the needle is believed fraught with danger. As is common, the plunger may be broken off at a weakened section and reinserted into the other end of the barrel. This device is also believed unnecessarily complex.
Gloyer U.S. Pat. No. 5,304,154 disclosed a retractable syringe with a needle holder in an articulating connection with a thin walled barrel. Protrusions in the needle holder and slots in the barrel together provide a mechanism for retaining and releasing the needle holder. This patent further discloses a plunger/needle holder single-use snap connection consisting of a protruding latch in the plunger and a corresponding cavity in the needle holder. Given the variations in wall thickness of the barrel section to provide the slots, and the complicated geometry of the needle holder cavity for the snap connection, this device is believed difficult and expensive to manufacture, and subject to quality problems.
A safety syringe for injecting or withdrawing fluids and avoiding inadvertent needle sticks after use includes a thin-walled cylinder or barrel fillable with the fluids, a generally cylindrically-shaped needle holder that slides inside the barrel, and a hollow needle attached to the forward end of the needle holder. The needle holder has a through passageway near its central axis, such that the needle and barrel are in fluid communication. The outer surface of the needle holder has a number of L-shaped grooves, and the forward end of the inner surface of the cylinder has a number of corresponding protrusions sized to be received by the L-shaped grooves, to releasably secure the needle holder to the forward end of the barrel.
The aft end of the needle holder has a generally cylindrically-shaped cavity with a number of upstanding webs or stops. The plunger at the forward end has a piston slidably engaged with the inner surface of the barrel, the piston having a rod extending to the aft end of the plunger. The forward end of the plunger further has an anchor while the aft end of the needle holder has a corresponding generally circular opening and latch sized to receive and retain the anchor inside the cavity of the needle holder upon insertion thereon and rotation of the plunger. The anchor has a plurality of flukes sized to catch on the stops or upstanding webs in the needle holder cavity as the plunger is rotated about its central axis; positioning the anchor to be engaged by the latch. Preferably, the latch is merely a portion of the opening of reduced diameter. The forward end of the piston rod may have a reduced cross section, preferably a notch, to facilitate breaking off of the plunger.
After use of the safety syringe the plunger anchor may be pushed inside the needle holder cavity and the plunger rotated about its central axis. Advantageously, if somehow inadvertently coupled together, the needle holder and plunger may be decoupled by rotating the plunger back the other direction and pulling the plunger anchor outside the needle holder cavity. Instead, going forward with retracting the needle, the plunger is further rotated and pulled back, moving the needle and holder inside the barrel. Then the plunger broken off at its reduced cross section, effectively disabling the safety syringe from further use. Optionally a removable cap may be taken from the aft end of the plunger and inserted into the open forward end of the barrel.
Preferably there is an O ring on the outer surface of the needle holder for sealing any gap between the needle holder and the inner surface of the barrel. Preferably there is another O ring on the outer surface of the piston for sealing any gap between the outer surface of the piston and the inner surface of the barrel.
Preferably the L-shaped slots have widened V-shaped entrances, for ease of receiving the protrusions in assembling the safety syringe. Preferably the protrusions are at the forward edge of the inner surface of the thin walled barrel, for ease of manufacture. Preferably the thin-walled barrel is a substantially constant diameter and thickness except for the plurality of protrusions.
Given the shortcomings of the prior art, further significant improvements to safety syringes are desirable.
It is an object of the present invention to provide a safety syringe that minimizes the possibility of inadvertent needle sticks;
It is an object of the present invention to provide a safety syringe that prevents reuse of the syringe after one use;
It is an object of the present invention to provide a safety syringe that is inexpensive to manufacture;
It is an object of the present invention to provide a safety syringe that is easy to make without quality problems;
It is a further object of the present invention to provide a safety syringe that is simple to use;
It is a further object of the present invention to provide a safety syringe with a cap to seal the barrel once the needle is retracted therein.
It is a further object to provide a safety syringe in which if the plunger and needle holder are inadvertently coupled together they may be easily separated.
These and other objects and advantages of the present invention will be apparent from a review of the following specification and accompanying drawings.